1. Field of the Invention
This invention is in the field of integrated semiconductor circuit elements wherein a diffusion barrier layer of tantalum disilicide covered on each side with a layer of substantially pure tantalum is disposed between the doped substrate and the aluminum or aluminum alloy interconnect level.
2. Description of the Prior Art
Integrated semiconductor component circuits are composed of multilayer structures formed of a great variety of materials. Contact must be provided between metal-metal, metal-insulator, semiconductor-insulator, and semiconductor-metal. In addition, structural defects such, for example, as grain boundaries and dislocations may exist in the layers. The close contact between the layers, the diverse nature of the materials, and the presence of structural defects are factors which provide problems at elevated temperatures and in the presence of external influences such as electrical voltages or high current densities. The interaction between the materials which sometimes occurs can seriously deteriorate the function of the circuit and reduce its reliability.
The problems become increasingly difficult with increased miniaturization where higher current densities occur, and the diffusion regions become flatter. Barrier layers must accordingly be introduced in VLSI (very large scale integrated) technology, to improve the reliability of the components at the contact surfaces by suppressing or reducing the surface reactions which can exist at those surfaces.
One of the critical boundary surface in components having structures measuring 1 micron or less are contacts between silicon and an aluminum alloy, for example, Al/Si, Al/Cu, Al/Si/Cu, or Al/Si/Ti. Since these contacts are exposed to temperatures up to 500.degree. C. during manufacture of the components and the aluminum-silicon eutectic temperature is only about 577.degree. C., an interdiffusion of the two materials into each other cannot be prevented to a depth of 100 nm or so. This effect is referred to as Al spiking and is described in the book "Thin Films Interdiffusion and Reactions", John Wiley and Sons, New York 1978, pages 15-25. The increasing current densities in the contacts additionally induce a silicon electromigration which leads to short circuits between the diffusion regions and the substrate. This effect cannot be eliminated by a silicon doping of the aluminum interconnect material.
Since the depth of the diffusion regions in the contact hole region only amounts to about 250 nm in VLSI components, there is the requirement that silicon diffusion into the aluminum, and aluminum diffusion into the silicon, can be tolerated only in the nm range.
The problem of obtaining a reliable contact between aluminum alloys and silicon has sometimes been resolved by separating the two materials from one another by means of a barrier layer. The functioning of such barrier layers is described in an article by P. S. Ho in "Thin Solid Films", Vol. 96 (1982), pages 301 to 316.
A barrier layer composed of a titanium-tungsten alloy is disclosed in an article by V. Hoffman in Solid State Technol., June, 1983, pages 119 to 126, and in an article by S. E. Babcock in J. Appl. Phys., Vol. 53 (10), October 1982, pages 6898 to 6905.
Further materials for barrier layers are disclosed in the following articles. A barrier layer of pure tungsten is described by D. L. Brors et al, in "Solid State Technol.", April 1984, pages 313 through 314. An article by C. Y. Ting et al in "Thin Solid Films", Vol. 96 (1982), pages 327 through 345, discloses a barrier layer of titanium nitride, as does an article by Wittmer in J. Vac. Sci. Technol. A2, Vol. 2 (1984), pages 273 through 279.
A disclosure of barrier layers of zirconium nitride will be found in Krusin-Elbaum et al "Thin Solid Films", Vol. 104 (1983), pages 81 through 87. A niobium-nickel alloy barrier layer is discussed by Wiley et al in IEEE Transactions of Industrial Electronics, Vol. 29 (1982), pages 154 through 157. Barrier layers of an iron-tungsten alloy are disclosed by Suni et al in "Thin Solid Films", Vol. 107 (1983), pages 73 through 80.
The materials mentioned above provide a low impedance contact to n.sup.+ silicon when a clean boundary surface, i.e., a boundary surface free of oxides and carbonaceous impurities is present. The disadvantage of the aforementioned materials, however, is that a reactive element, referred to as a silicide-forming agent, is necessary for the reliable manufacture of a low impedance contact as described in J. Vac. Sci. Technol. A1, Vol. 2 (1983), pages 459 through 462. This can lead to a diffusion of silicon out of the contact hole at elevated temperatures, even as low as 450.degree. C.
An article by Fraser et al in J. Vac. Sci. Technol., Vol. 18 (1981), pages 345 through 348, sets forth that very low impedance contacts can be obtained by employing tantalum silicide in combination with polycrystalline silicon as a gate contacting material. When other materials are to be utilized therein as diffusion barriers, as outlined above, this means an increased manufacturing expense.